Dressing mechanism



July 16, 1935. R. s. CONDON ET AL DRESSING MECHANISM Filed Oct. 27, 1932 2 Sheets-Sheet 1 lnmmorf @bf' '57 am cvzci Chem TGLZZZW non leg Juiy 16, 1935. R. s. CoNDoN El A L DRESS ING MECHANI SM Filed Oct. 27, 1932 2 Sheets-Sheet 2 2 a i 1 w y a 5 a m y a m y 5 a 5 y w 5 n 3nventor; .li'ober'i J C QnCZOn and ttorneg Patented July 16, 1935 UNITED STATES:

PATENT OFFICE DRESSING MEoirAm Robert S Condon and Clarence ,Galloway; Rochester, N. Y., assignors toG leason Works, Rochester, Y., a; corporation of New York Applicationoctob'er 27, 1932, Serial No. season 18 Claims. (oi. 125-11 rocating truing tool turns a continuous helix on the surface of a grinding wheel and the smoothness of the surface ground by the wheel depends directly on how fine and how uniform is the lead of this helix. In hand-operated dressing mechanisms, as heretofore built, thehuman element has always entered too much into the dressing operation and it has been extremely difiicult to get satisfactory results especially where precision grinding was desired. At one time, an operator would move the truing tool across the grinding wheel faster than at another time and no opera' torsnerves Were ever so steady that he moved the truing tool across the whole face of the wheel at an absolutely uniform speed. i

Another objection to hand-dressing mechanisms of previous constructions has been the loss of time of the operator in the dressing operation. The operator has had to manipulate the tool to effect the dressing operation and, therefore, the time required for dressing has meant time. that could not be devoted to other work. i i

The primary purpose of the present invention is to provide a manually-controlled dressing mechanism in which the human element is entirely eliminated as a factor in the dressing operation.

A further object of the invention is to providei. a dressing mechanism in which the fineness of i dressing can he predetermined and is not depend an extended period without attention; In this connection, it is afurther purpose of the invention to incorporate into a dressing me hanism, means for sending a blast of air through the rela-' tively movable parts, each time thedre'ssing mechanism is operated; thereby blowing grit and dirt out from between the parts. m Another object of the invention is to provide a dressing mechanism whichwill be extremely com-f pact and which will occupy a minimum of space; so "that it can-be readily used on'eiiis'tirigmachiries ually adjustable throttle valve. movement of the truing' tool or tools across these without interference with the operation of such machines H g V Another object of the invention is to provide a dressing mechanism which an operator may put into operationsimply by movement of an opera t-.

ing handle and which will then complete the dressing cycle without'further attention from. the

operator. v i

Still another object of the: invention is to provide a fluid-pressure operated dressing mechanism'in-which a pair of dressers can be so coupled together that a 'single control valve can be em ployed to control theoperation of both. 7 p

A further objectof the invention is to provide a dressing mechanism in which the dressers for truing a side and the tip surface of a grinding wheel are carried on the same part and operated through a singlemechanismand by a single movement, thus eliminating one of the dressing units heretoforerequired for dressing thesurfaces 20 of a grindingwheel and reducing the cost of a cbmplete dressing unit and rendering the unit more compact;

Thedres'sing' mechanism of the present invention differs from previous dressing mechanisms in that, while manually controlled, it is actually operated automatically. The movement of the, truing tool across the face of the wheel takes place underhydraulicpower. The human element is entirely eliminated and a smooth and uniform movement of the truing tool across the grinding wheel is insured without the cost and complication of an automatic dressing mechja mm. A manually shiftable reversing valve controls'the reciprocation of the truing tool or tools across the side or' sides of the grinding wheel. whilelthe'desiredjrateof travel of the'truing tool or tools'across the' wheel iscontrolled by aman- The rate "of grinding wheel can'he predetermined exactly by adjustment of the throttle valve and is entirely independent'ofthe skill of theoperator. V The'reversing valve is a sliding valve and is shifted by movement of an operating handle c1 knob securedthereto. Through an ingenious ar rangement thethrottlej valve can be adjustedby rotating this same knobor handle.

The truing toolis's'ecuredto the head of a piston rodthat is hydraulically reciprocated under control of the reverse and throttle valves. To'obtain compactness together with strength and riggidityi thepistonrod"isfmountedto "reciprocate in aaeceemnqasm provided" in; arelatively fixed;

guarantees a support an the ailing toolis guided in its reciprocation by a key that engages in a longitudinal slot cut into the guide member or support at its thickest part, that is, cut into the periphery of the guide-member at the point most remote from the center of its bore. The key is carried by a skirt or sleeve that is connected to the head of the piston rod and that surrounds the guide member.

Telescoping guards are provided to prevent entry of water or grit into the parts as the truing tool reciprocates back and forth. As a further means of protection, the device already referred to is provided for blowing out the guards automatically each time the dressing mechanism is operated, There is a valveinounted in the relatively fixed guide or support; Thisgvalve is so constructed that when the truing tool moves outwardly across the grinding wheel, air is drawn in between the skirt of the piston rodheadand the rod or support, and, when the truing tool makes its return stroke, the valve is substantially closed and this entrapped air is forced out between the parts of the telescoping guards, blowing grit and water out.

, In one embodiment of the invention, as mentione'd above, the operator is only required to push the reverse valve in to start the truing operation and the rest of the operation will be completed without his further attention. When the reverse valve is pushed in, hydraulic pressure is applied to one side of the piston to which the truing tool is connected and the truing tool is moved across the face of the grinding wheel. The exhaust fluid from the other sideof the piston operates a hydraulic load and fire mechanism. When the truing tool has traveled across the face of the grinding wheel, this load and fire mechanism is tripped and the reverse valve is reversed. This causes the 'truing tool to be returned to original position clear of thewheel and the truing operation is thus completed. When this embodiment of the invention is used, it takes but a'sec- 0nd for the operator to start the truing mechanism and he is left free to attend to the grinding machine or to take care of other duties in connection with his work.

' in the stroke of the reciprocable part allows'the tip truing tool to remain in engagement with the grinding wheel long enough to true up-the tip surface of the grinding wheel. As against previous constructions, this improvement eliminates one truing unit entirely, namely, the tip truing unit, with the resultant important gainin com- 'pactness. Space is always a vital factor within a grinding machine.

The principal features of the invention have been referred to above. The invention includes,

however, several further constructional improvements that will be apparent hereinafter from the specification and from the recital of the appended claims.

In the drawings:

Figure 1 is a view illustrating somewhat diagrammatically one embodiment of the present invention and showing in section thereverse valve and the dressing unit and further illustrating in dotted lines how a second dressing unit might be coupled into the system so that two units for dressing opposite sides of a grinding wheel can be controlled simultaneously from a single reversing valve;

Figure 2 is a View showing another embodiment of the present invention in which means are incorporated enabling the dressing mechanism to complete its cycle automatically once the reversunits are shown coupled together and in position for dressing'opposite sides of a grinding wheel,

and one of the units includes both a side and a tip truing tool. Further, this figure shows an arrangement wherein the side truing tools move simultaneously in opposite directions;

Figure 3 is a diagrammatic view on a reduced scale showing how the reversing valve and dress Figure 6 is an enlarged fragmentary View showing the breather valve which controls admission of air between the reciprocating parts during operation of a dresser unit;

Figure '7 is a fragmentary plan view, showing the cylinder-end of one of the dresser units; and

Figure 8 is an end view of the trip-lever, which operatively connects the load and fire mechanism with the reverse valve.

In the drawings,I have shown several different embodiments of my invention. The same dressing unit can be employed in all the various embodiments of my invention. If it is required to dress two sides of a grinding wheel, the dressing unit employed for dressing one side of the wheel can be duplicated. This is true regardless of whether the two dressing units be arranged to move simultaneously in opposite directions or simultaneously in the same direction.

Referring then to the drawings by numerals of reference, It] indicates a support or guide constituting a relatively fixed part of a dressing unit constructed accordingto the present invention. The support It] is formed to provide a cylinder i I and a cylindrical extension or guide I 2. The extension or guide i2 is bored eccentrically of its periphery, as'clearly shown in Figure 4.

A piston I4 is mounted to reciprocate in the cylinder H and to the piston i l there is secured by a nut IS a piston-rod l5. The piston-rod projects forwardly through one end-wall of the cylinder I I into and through the eccentric bore of the guide-extension (2. The piston-rod is of a diameter to fit snugly the bore of the guide-extension so that the part !2 serves as a bearing and support for the piston-rod in its movement.

The piston-rod I5 is formed with an enlarged head at its outer or forward end and to this head there is secured a sleeve or skirt IS. The skirt is held in position by a nut H which threads onto a stud I9 that is integral with the piston-rod IS. The sleeve or skirt I8 is tubular in shape and fits over and telescopes on the guide-extension l2.

There is a peripheral groove 26 out longitudinally in the guide-extension i2 at the thickest portion of the same, as shown in Figure 4. There is a key 2| secured by screws 22 to the skirt I8. This key engages in the groove 20. A longitudinally taingvalve is tripped. In this figure two dressing pering gib 23 is also mounted in the groove 20 and can be adjusted by the screw 24 to take up wear of the groove and key.

By providing the eccentric bore in the extension l2, the groove 20 can be made of the requisite depth without weakening the extension and sothe dresser unit can be kept'quite compact. If the extension were bored centrally for the pistonrod l5, the extension would have to be of considerably larger diameter to permit cutting a'ke'yway init and thus the size of the wholc iuiit would be increased.

In Figure 1, 25 designates a diamond dressing tool such as is commonly used in dressing mechanism. The tool is mounted for rotatable adjust ment in a lug 24 formed integral with a plate 26 and the plate 26 is fastened by screws 21 to the head of the skirt [3. at one side from this plate 26 in position to dress the side of a grinding wheel on reciprocation of the piston I 4.

In Figure 2, one of the dressing units is shown arranged to carry both a side dresser and a tip dresser. The side dresser is again designated as 25, while 28 denotes the tip dresser. The plate 29 which carries the two dressers 25 and 28 is of a different shape from the plate 26 which is intended to carry the single dresser. The plate 29 is provided with an arm 3!] that extends a considerable distance forward from the plate. The side and tip dressers are bothmounted in this arm. The side dresser 25 is rotatably mounted in the forward end of the arm in a manner similar to its mounting upon the plate 26.

The tip dresser 28 is here shown as having a conical operating surface and as being threaded into the arm 3E! for adjustment thereon axially of its conical operating surface. To permit precise adjustment of this tip dresser 28, it may be adjusted against a stop-screw 3| that is threaded into an arm 32 also formed integral with the plate 29.

The tip dresser 28 may be made of carboloy or a similar material embedded with small diamonds or it may be made of some hard material like carborundum. The operation of the tip dresser will be described more particularly hereinafter.

The dressing units are hydraulically operated. We shall first describe the operation of the em.- bodiment shown in Figure 1. Here the operation of the dresser unit is controlled by a reverse valve 35. This valve 35 is mounted to slide in a sleeve 36 that is secured in a valve-casing 31.

The valve 35 is provided with spaced peripheral grooves 38, 39, 49, 4| and 42. The'sleeve 36 is likewise provided with spaced peripheral grooves 44, 45, 46, 41 and 48. Each of the grooves 44, 45, 46, 41' and 48' is connected with the bore of the sleeve by a series of radial ducts that are drilled from the interior of the sleeve into the grooves. The ducts that connect the groove 44 with the interior of the sleeve 36 are designated at 50, the corresponding ducts which cooperate with the groove 45 are denoted at 5!, while 52 53 and 54, respectively, denote the ducts leading from the grooves 45, 41 and 48, respectively.

The valve stem 35 is provided with a central bore or duct 55. This cornmunicates'with the groove 39 through radial ducts 56 and with the One end of the bore is formed with a seat for a ball -relief valve Biwhich'is pressedto closed position'by the spring BI.

thread adjustably into the bore59.

The diamond 25 projects The valve stem 35 is also provided with a bore?- 59 which is in alignment with the bore 55. When the throttle valve 58 is open, fluid can flow from the duct 55 through the throttle valve opening into the bore'59 and thence through radial ducts 60 into theig'roove 42 in the valve stem.

The throttle valve 58 is integral with a rod 62' that is threaded for aportion of its length to The rod 62 carries a; pin 63' at its rear end that engages in a longitudinal slot 54 formed in the valve-cap 65 to hold the rod 62 against rotation relative to the valve-casing 31. By rotating. the valve. stem- 35, then, the amount oil-opening of the throttle valve 58 can be adjusted to control the rate of movement of the dressing diamond or diamonds across the face of the grinding wheel, as will hereinafter be further described. To insure accurate adjustment of the throttle valve, a graduated dial 65 is provided. This dial is secured to the valve stem 35 by a set-screw 66. The graduations of this dial read against a pointer 61 that is secured in any suitable manner to the valvecasing 31. i i

The reverse valve is operated by pushing or pulling the knob 68 thatis secured in any suitable mannerto the valve stem 35. The groove 64 is long enough for the pin 63 to remain in engagement with it throughout the whole of the movement of the valve stem in either direction.

Spring-pressed detents are provided to hold the valve stem at either limit of its reciprocating movement. These may take the form of balls 10. The valve stem is provided at its inner end with an enlarged head i I. This head is beveled off as indicated at '12 and is provided with a V-shaped roove as indicated at 13. The sleeve 35 is provided at its inner end with an enlarged head 15 that engages a shoulder formed interiorly of the valve casing 31 to hold the sleeve against axial movement in one direction in the casing. The end of this head 15 is beveled oii as indicated at 76; The balls 10 are mounted in holes drilled in the valve-casing and are pressed interiorly of the casing by the coil springs 18 which are interposed between the balls and the plugs 79- which thread into the casing. The springpressed balls will ride on the sides of the groove 13 and the side of the bevel l2 and hold the valve stem resiliently in either limit of its movement.

The valve casing 31 is connected with an oil pump or other suitable sort of fluid supply by the pipe 30; The pipe 8! is an exhaust line leading from the valve casing back to a sump. The valve casing is connected with the cylinder H by fiexible'piping 82 and 83. Thepiping 83 threads at one end intoa cap plate 84 that closes the outer end of the cylinder H and is secured to'the support Ill by screws 35. At its other end the piping :82 threads into the valve casing 31 and communicates with the groove 4! of'the sleeve 38. The piping 82 also threads at one end into the cap-plate 84. It communicates with a duct 85 (Figures 1 and 7) and also with a; duct 81 that leads into a duct 88 that extends parallel to the duct 85. A duct 98 leads from] the duct 85 into the cylinder H at a point intermediate the ends of the cylinder. A duct 9! leads from the duct 88 into the cylinder II at l 1 end; theqpiping 82, threads into th'e" casing .31

at a pointv to communicate with the groove 45 of the sleeve 36. v "A ball-check'valve 95 is provided in the duct 86 to prevent flow of fluid through said duct in one direction. The ball-check valve is DOT-r mally held in operative position by the coilspring 96.

'In the position of the parts shown in Figure 1, the motive fluid flows from the supply line 80 through the groove 46 and ducts 52 in the sleeve 36, the groove in the valve stem 35, the ducts 5i and the groove of the sleeve36, the piping 82, ducts ill, 88 and 9| into the forward'end of the cylinder H, forcing the piston l4 rearwardly in the cylinder to traverse the diamond 25 in one direction across the side surface of a grinding wheel. At this time, the fluid exhausts from the rear end of the piston l4 through the piping 83, the groove ll and ducts 53 of the sleeve 35, the groove 4! and ducts 51 of the valve stem 35into the duct 55 of this stem, forcing the throttle valve 58 open to the extent allowed by the adjustment of the rod 62, and flowing through the ports 59 of the valve stem, the groove 52 of the valve stem, the ducts 54 and groove 48 of the sleeve 36'into the line 8| whence the exhaust fluid returns to the sump.

When the knob 68 is pushed inwardly, the direction of travel of the diamond 25 is reversed.

' The motive fluid will then flow from the supply pipe through the groove as, ducts 52, groove 40, ducts. 53, groove 4'! and piping 83 into the rear end of the cylinder H, forcing the piston I 4 forward in the cylinder. At this time, the fiuid exhausts from the cylinder it through the ducts and 9|, 86, 88 and 87,-the line 32, groove 45, ducts 5|, groove 39, ducts 56 into the duct 55. The pressureof the liquid will force the relief valve 6| open and the liquid will then flow through the throttle valve 58, ducts to and 54 and groove 48 into the exhaust line 8|.

'As the knob 68 is pushed inwardly, as described, the balls 1&3 roll up out of the groove 73 and drop behind the bevel l2, holding the valve stem in its rearward position. With the construction shown in Figure l, to reverse the valve again, it is necessary to pull the valve stem outwardly by grasping the knob t8 and pulling thereon. This will cause the balls "iii to ride up the bevel l2 and drop back into engagement with the groove 13.

It will be noted from the preceding description that the relief valve M operates in only one direction of movement of the piston I l. The purpose of providing this relief valve istomake the pressure on one side of the piston when it is moving in one direction equal that on the opposite side of the piston when it is. moving in the opposite direction so that the dressing diamond will move across the grinding wheel at the same rate in either direction of its movement. The effective area of the piston is less on its front side than on its rear side because the piston rod I5 is secured to the front side of the piston. The relief valve hi acts, however, to resist forward movement of the piston. By using a spring 6| of the proper tension, enough resistance can be built up against the forward movement of the piston so that despite the greaterfefiective area of the rear'side of the piston, the pistonwlll not move forward in the cylinder by pressure on its rear face faster than it will move rearwardly by pressure on its front face. If a difference in rate of movement of the this recess.

diamond opposite directions is of no moment,-

the. relief valve 6| can be omitted.

The ball-check valve has no special function when a single dresser unit is employed and it is ordinarily preferred to omit it in a single dresser unit. .Its purpose will appear-hereinafter in the explanation of the operation of the are provided to protect the dressing unit of the The telescoping guards are clearly shown in Figure 1. There is a tubularguard Hill secured in any suitable manner to the sleeve or skirt l8 and there are two tubular guards Hit and IE2 secured in any suitable manner to the support Hi;

The guards HH and 32 are of such diameter and so spaced from one another that the guard I69 will telescope between them and the guard llH- is also of such diameter that it will surround the skirt l8. Felt rings led may be inserted in the skirt is to further help seal and protect the piston rod l5 andguide As a still further protection, a breather valve is mounted inthe support Hi.- This valve comprises the sleeve H35 (Figures 1. and'G seat Hi5 and disc H31. The sleeve Hi5 threads into a hole in the support 80 and serves to hold the seatlilii against a shoulder on the support it. The seat Hi3 has a recess 58 in its bottom face and the disc Sill fits into The depth of the recess M38 is suflicient to permit the disc it? to move freely up and down in the recess. v

The sleeve IE5 is hollow and communicates with the outer air through the opening 09. The seat Hi6 has a'central opening HQ extending therethrough and the disc H5! is also provided with a central aperture HI of much smaller diameter than'the opening 5 ill in the seat It.

Two ducts I I2 and 1 l3 are formed in the casting !0 and lead from-the seat m5 at diametrically opposed points. These ducts communicate with a duct H4 that extends into the pocket formed When the piston l4 moves to. the right in the cylinder l I, air is drawn from the outside through the opening H19; the bore of the sleeve M5, the

duct H0 in thevalve seat and around the disc I91 into the ducts H2 and H3 and'thence into the pocket between guard l8! and the cylindrical guide or support l2. When the valve stem 35 is reversed and the piston M moves to theleft, the disc Itll is forced against the seat Hi6 and the air, previously entrapped can only escape throughthe very small opening I l i in the disc lll'l. It is therefore forced forwardly be tween the guard and the skirt l8 and thence between the guard 553i and the guard H26 and thence between the guard Hi9 and the guard H32.

Air is thus blown through this circuitous passageand any dirt or grit or water that might have.

gotten between the guards as they extended is blown out as they telescope again.

In most cases, it is desirable to leave a small opening Ill in the disc IO'I to prevent building up of excessive pressure when the guards telescope together, but, if desired, the opening II=I might be omitted entirely.

Packing H5 is provided to preventleakage of oil from the cylinder H along the piston rod I5, while packing I i5 is provided to prevent leakage of oil along the rod 62. The nut In which threads into the head II of the valve stem 35 serves to hold this latter packing in position.

Oil leaking outwardly along the valve stem is returned to the sump through the ducts 50, groove 44 and leak-return pipe H8.

Where it is desired to dress two sides of a grinding wheel as required, for instance, in the case of wheels for grinding gear teeth, two of the dresser units may be coupled together and controlled by a single reverse .valve anda single throttle valve. One method of so coupling two dressing units together is illustrated in Figure l, where I have shown a second dressing unit coupled in circuit with the unit already described in such manner that the two dresser diamonds move simultaneously in opposite directions. The second dresser unit is shown in dotted lines. The two dresser units shown are absolutely iden'- tical in construction, but for the purpose of more readily describing their operation, I have designated parts of the second unit by primed reference numerals.

To operate the two dresser units, the line 82 is extended, as shown in dotted lines at 82, into the rear of the cylinder I I instead of connecting with the duct 86 drilled in the casing 1.. The two ducts 35 and 85' require also to be connected as by the dotted pipe line I20.

When the valve stem 35 is in the position shown in Figure l, the pressure fluid will flow from the pipe line 82'-B2 into the cylinder II forcing the piston I l forward and moving the diamond to the right. The fluid exhausting from the fron end of the piston I4 flows through the ducts 85' and 88' into the line I23 whence it flows through the ducts 86, 88, 99 and SI into the front end of the cylinder I I, forcing the piston I4 rearwardly in this cylinder and moving the diamond. to the left. The exhaust fluid flowing from the rear end of the cylinder -II passes through the line 83 to the valve casing 31,

whence it returns to the sump. When the valve is shifted, by pushing in the knob 68,-the pres sure fluid flows through the line 83 into the rear of the cylinder I i, moving the piston I4 and dresser 255 to the right. This forces the fluid out of the front end of the cylinder II through the ducts 9i and 9!, 85 and 88 into the line I20 whence it is carried through the ducts 88 and 9! (the valve 95' being forced shut) into the front of the cylinder 5 1. Thus the piston I4 is forced rearwardly in the cylinder II and the diamond 25' is carried to the left. The fluid in the rear of. the piston it at this time exhausts through the line til-82'. Thus with the piping arranged as described, the single reverse valve controls the two dresser units and the two ressers move simultaneously in opposite directions.

When a single dresser unit is used, the motive fluid will flow from the source of fluid supply alternately to the front and rear ends of the piston I4. Thus the two chambers. formed in thecylinder I Ion the opposite sides of thepiston I4 are alternately'filled with 'oil from the source of fluid supply. When two dresser units are used,

however, and coupled together in the manner shown in Figure 1, .the front ends of thetwo pistons I4 and I4. are not connected directly to the source of fluid supply} If no ball-check valves 95 and 95' were used, no pressure fluid would ever get into the front ends'of the pistons I l and I I, save that which would leak by these pistons in their movements, and the two pistons in their forward movements would simply be compressing what air was entrapped between the pistonsand the forward end walls of the cylinders II and II, respectively. The ,air entrapped in the forward ends of. the two cylinders or the oil that would leak past the two pistons into the forward ends of the two cylinders, would never operate the two dressing units with precision. The pistons probably would not move fully to the left on their return strokes and where it was possible for varying amounts of fluid to leak past the pistons, the strokes of the pistons would vary in length depending upon the amountof leakage.

To insure uniform and full strokes; of the two pistons at all times, the ball check Valves and ducts 86-90 and 86' 9Il are provided. The first time the mechanism is operated, the air in the front end of the cylinder. II may be compressed, but the pressure fluid willforce the piston l4 far enough forward in the cylinder II to clear the duct 90, and thenthe pressure fluid will flow through the ducts 90 and 86, forcing the ball check valve 95 open and flowing through the line I20 and ducts 81,88 and 9! into the front end of the cylinder I I. Thus the piston I I will be forced rearwardly in the cylinder II, not by air compresedin the front end of the cylinder I I, but by pressure fluid delivered directly from the pump through the ducts 90' and 86' and the ball check valve 95".

Similarly, when the valve stem 35 is reversed, the piston I4 will be forced forward in the cylindei II far enough to clear the duct 90 and the pressure fluidwill then flow through that duct and the duct 86, opening the ball check valve 95 and flowing through the line I20 and ducts 88' and 9| into the front end of the cylinder II.

Thus, by use of the two ball check valves in conjunction with ducts 9B and 90', which enter the two cylinders at points intermediate to the ends of the two cylinders, assurance can be had that the motive fluid will flow to both sides of the pistons I4 and I4 and that these pistons will be operated uniformly. Of course, to insure this uniform operation, it is desirable to eliminate any air" entering the system. i This can be done by simply opening the plugs 92 and 93, 92' and 93' slightlyand operating the pistons a few times until the air is forced out of the pistons and oil begins to seep out the plugs. Then'when the plugs are. tightened, the system will be free of air.

With a reverse valve built and operated as described withreference to Figure 1, the operator of themachine must push the knob 68 in to move thediamonds in one direction and pull the knob out again to move the diamonds in the opposite direction. I This is an improvement over manually operated dressers, as heretofore constructed, for previous dressers have required that the operator actually move the diamonds acrossthe grinding wheel. Where the wheel can be dressed by a single passage of the diamond across its face and where the diamond can be moved far enough in this passage to clear the wheel, the construction of Figure 1 can be used advantageously, but where the diamond. must be passed twice across the wheel-to complete the dressing. or must be returned to initial position to clear the wheeL-the construction of Figure 1 has its limitations, so

for as efficiency is concerned, because the operator is required to manipulate the reverse valve twice tocomplete the dressing cycle. V

Where an operator is attending a number of machines, a considerable gain can be achieved if provision is made whereby, once the dresser is put into operation, it will complete its cycle of operation automatically. Such an imrovement in construction constitutes one of the principal features of the present invention and will now be described.

The reverse valve stem shown in Figure 2 and the sleeve in which-it slides are of identical construction with the valve stem and sleeve shown in Figure 1, except that there are a pair of pins I25 (Figures 2 and 8) mounted'in the head H of the valve stem, one at either side of the rod 62. The valve and sleeve are simply shown in elevation in'Figure ,2, whereas they are shown in sec-' I in the cylinder I32; This piston is formedwith an integral rod or stem I36, that is hollow, and

is adapted to extend into the bore I33. There is a plunger I31 mounted to reciprocate inthe bore I33; This plunger telescopes at one end into the bore of the piston rod I36and engages at its other end the arm I39 of the lever I26. A coiled spring I40 that is mounted in the bore of the piston rod I36 serves to urge the plunger I31 in p a direction outward of the bore of this piston rod. There is a disc I38 carried by this plunger, the purpose of which will appear hereinafter.

Oneend of the cylinder I32is closed by the plate I42 whichis securedin any suitable man ner to the casing I30. To'prevent leakage of oil along the piston rod I36 through'the other end of the cylinder, a packing I43 is provided.

The pressure fluid ispumpe d' to the casing through the pipe I45 which takes theplace of thepipe 80 of Figure 1 and isconnected to the casing I30at a point corresponding to thatat which thepipe 80 enters the casing 31 of Figure l. The exhaustfluid flows from the casing I30 through the pipe I46 which corresponds tofthe pipeiil of Figure 1 and is connected. to the casing I36 at a correspondingposition. The ducal communicates with the sleeve 36 at the same point that the pipe 83 communicates with the sleeve 36 in Figure 1. This duct I41'is connected with the piping I48. At a point corresponding to where the pipe 82 enters the casing 31 of Figure 1, there is a duct I50 in the casing I30 of'Figure 2. This duct communicates with the cylinder I32 through the ducts I5! and I52 and theport I53 drilled in the casing I30. There is a line: I55

' leading from one of the dresser units to the other end of this cylinder I32. The two dresser units are alsoconnected by a line I56.

When the parts'are in the position shown. in

Figure 2, the duct I50 will be on supply from the line I ts-because of the position of the reverse valve 35. v The pressure fluid will flow through the ducts I50, I5I and I52 and the port I53 forcing the piston I35 to the left in the cylinder I32 as shown. Oil in the left end of the cylinder I32 will be forced out of the cylinder through the:

line I55 into the cylinder II, forcing the piston I4 forward in this latter cylinder and carrying the diamond 25 across-the outer side surface I of the grinding wheel W; The movement of the piston I4 forward in the cylinder II, will force. the fluidin the cylinder 1 I in front of the piston I4 out through the ducts SI and 36, 88' and 36' and the check valve into the line I56, whence it passes through the ducts 83 and 9! into the front end of the cylinder II. Hencethe piston I4 is moved rearwardly in the cylinder I I and the dresser 25 is moved backwardly across the inside surface l6i of the grinding wheel W. The movement of the piston I4 rearward in the cylinder I I forces the fluid behind the piston out through the line MB and duct I 31 into the valve casing whence it returns through the throttle valve 56, as described with reference to Figure l, and pipe I46'to the sump.

When the operator pushes the knob 68 in wardly, the direction of application of iluidprew sure through the pistons I5 and I4 will be reversed, as described with reference to Figurel. Also when the valve stem 35 is pushed inwardly, the pins; 225 will rock the lever 26 about its pivot pin I21 against the resistance of the spring I40. The plunger I31 will, therefore, be pushed into the bore of the piston rod 133 and the spring I 40 will hecompressed. The plunger I31 will be resiliently held in this last described pos'ition because when the valve stem 35 is pushed inwardly, the detents 16 will ride up out. of the groove '13 anddrop behind the bevel 12 of the head of the valve stem.

Having pushed the valve stem in, the operator can go away and leave the dressing mechanism and it will perform its cycle without his further attention. When the valve stem is pushed inwardly, as described, line I48 will be put on supply. The piston I4 will move forwardly in its cylinder I I, moving the diamond 25 forwardly across the inside surface I61 of the grinding wheel W. The fluid in the forward side of the piston I4 will be forced out of the cylinder II through the ducts 63, 91, 86 and 88, into the line I56 and thence through the ducts 68' and BI into the front ends of the cylinder II. This will move the piston I4 rearwardly in its cylinder drawing the diamond 25' rearwardly across the side face I63 of the grinding wheel. fluid forced out of the rear end of the cylinder II' in this movement will flow through the pipe I55 into the cylinde" I32. This will force the piston I'35'to the right in this cylinder, further compressing the spring I46 which, as already described, is already compressed somewhat because at this time the plunger I31 is being held over to the left fr-omthe positionshown in Figure 2 by the lever I26.

As the piston I35 continues to move to the right, the spring I40 .will be compressed still further until the right end of the piston rod I36 strikes the disc I38 carried by the plunger I31. Then the plunger I31 will be moved on to the right with the piston I35. This will rock the lever I 26 about its pivot i21 back to the position shown in Figure 2. The ball detents 15 will ride up the bevel 12 and the reversing valve will be returned to the position shown in Figure 2. As soon as the ball detents have cleared the bevel The "I2 and are riding .on the flat I62 between the bevel I2 and the groove I3, the spring I40 will come into action and push the reverse valve quickly on back to the leftward position shown in Figure 2. a

The return of the reverse valve to the position shown in Figure 2 will put the duct I56 again on supply and the line I48 again-on exhaust. The pressure fluid entering the cylinder I32 through the port lei; will force the piston I35 back to the left to the position shown in Figure 2. The fluid forced out of the left end of the cylinder I32 by this leftward movement of the piston I35 will flow through the line I55 into the cylinder ii and the diamond 25 will be moved forward across the grinding wheel to return to the position shown in Figure 2 and moved far enough forward to clear the wheel. The fluid forced out of the front end of the cylinder II in this movement will flow through the 'line I56 into the front end of the cylinder II. The diamond 25 will be drawn back across the grinding wheel and returned to the position shown in Figure 2. The fluid forced out of the rear end of the cylinder ii in this movement will pass through the reverse valve and the throttle valve into the exhaust line I 46.

The dressing mechanism will now have completed its cycle. As indicated, all that it is necessary for the operator to do is to push the re verse valve inwardly and the two diamonds will be passed back and forth across the two sides of the grinding wheel and the parts returned to intial position without any further attention on his part. For fine work, the throttle valve58 will be adjusted to allow only a very slow exhaust in order to obtain a very slow travel of the diamonds across the face-of the grinding wheel. But the slowness of their movement does not interfere with the work of the operator. He can attend to other duties. Even if he has only one machine to operate, the use of the dressing mechanism disclosed in Figure 2 will render him more efficient for during the dressing interval, he can remove a completed workpiece and chuck a new blank in place on the grinding machine.

Where only the sides of a grinding wheel are to be dressed, the diamonds ,need only be moved across the grinding wheel in one direction far enough to dress the side for the full length and may then be returned to initial position. When it is desired to dress the tip of the grinding wheel also and the tip dressing tool is mounted .on the same support with one of the side truing tools, as is the tool 28 of Figure 2, then a dwell must occur at the end of the forward stroke of the piston I4 and this dwell must be of suflicient duration to permit the tip of the wheel to be dressed.

To secure this dwell, the cylinder I32 is made longer than the cylinders II or .I I if the three cylinders are of the same diameter. Thus, after the pistons i6 and i4 have bottomed in their respective cylinders at the ends of their strokes, the piston I35 will still have to travel some dis.- tance before the piston rod I36 engages the disc I 38 and trips the reverse valve. The distance. of this overtravel of the piston I35 determines the length of the dwell of the tip-dresser 2 8 in one gagement with the grinding wheel.

Where the piston @353 has this-overtravel, a greater volume of fluid is required to move the piston to either end of the cylinder I32 than can be contained in eitherthe cylinder 14 or .II. To insure that the piston I35 .be moved in .both directions to the full extent of the stroke, a sec- 0nd ball-check valve and overflow duct must be incorporated in each truing unit.

For this purpose, the top-plates I65 and I65 of the two dressing units shown in Figure 2 should be drilled to provide ducts I66 and I66, respectively. The casings I6 and II! should also be drilled to provide ducts I 6? and I61, respectively, and ducts I68 and I68, respectively, which communicate therewith and which lead into the cylinders .II and .II', respectively, at points removed from the rear .ends of said cylinders at distances greater than the thickness of the pistons I4 and I4. Ball check valves I69 and I69 operate in the ducts I67 and l6l, respectively, and are normally held closed by springs I16 and H6.

With this modified construction, when the piston I4 has bottomed in the rear end of the cylinder II, the pressure fluid flowing into the front .end of this cylinder will continue through .the .duct I68, ball-check valve I69 and ducts I61 and I65 into the line 155, driving the piss ton I35 onto the limit of its movement to the right in the cylinder I32.

When the piston .i35 moves back to the left t the position shown inv Figure 2, the fluid in the cylinder I32 .on the left-hand side of the piston I35 isforced out of the cylinder. Since the cylinder I32 has a greater capacity in volume than the cylinders Ii and H, the excess fluid must be taken care of. The valve I69 in the dresser unit .Ill does this. The fluid that is flowing out of the left end of the cylinder I32 passes through the line IE5, forcing the piston i6 forward in the cylinder H. After the piston M has bottomed in the cylinder I i, the excess fluid flows through the ducts 96 and SI and connecting ducts into the line I56 and thence through the .duct 88 and duct 96 into the cylinder II, forcing the piston 14 rearwardly inthis cylinder. After the piston I4 has bottomed in the rear end of the cylinder II, the excess fluid will pass off through the duct I68, valve 169 and ducts 1.6,! and 166 into the line I46, whence it will return through the reverse and throttle valves to the sump.

When the dressing mechanism is arranged .to provide a dwell at the end of the stroke .of the side-trimming .diamond as described, the diamond25 will be carried across the side .I6'I of the wheel W and when the piston I4 has bottomed in the forward end of the cylinder II, the tiptnimming tool 28 will engage the tip surface 116 of the wheel. The tipetrimming tool 28 will remain in engagement with the wheel until the piston I35 has moved fully over to the right and tripped the reverse valve. Thus depending upon the dimensions of the cylinder E32, the tip-trimming tool .28 .can be caused to remain in engagement with :the tip of the grinding wheel for more or less time, as may be required, to true the tip surface of the wheel satisfactorily.

Preferably, the diamond 25 and truing tool 28 be spaced far enough apart to allow the diamond 25 to clear the side I6! of the wheel before the truing tool 28-actually engages the tip surface I IIl of the wheel;

The tip-truing tool 26 may be made of any desired shape. If the tip surface I'I of the wheel is to be inclined at other than a right angle to the axis N2 of the grinding wheel, a conical .truing tool such as shown as '26 is preferred. When the tip surface of the wheel perpendicular to its axis, ,a cylindricalrtip truing tool might be substituted for the conical tool .28 and ,used directly in place of the tool.28. As stated, however, the shape of the tip truing tool may be chosen at will to serve the purpose for which it is intended.

In Figures 1 and 2,, the dressers are shown coupled together to move simultaneously in opposite directions. Figure 3 shows diagrammatically how they might be coupled together to move simultaneously in the same direction. The same reference numerals heretofore used are employed in Figure 3 to designate like parts.

When the pressure fluid is flowing through the line il'5, the piston I4 is forced to the rear in the cylinder H and the fluid in the rear end of this cylinder is forced out through the line I16 into the fcrward'end of the cylinder ll. This forces the piston M also rearwardly in its cylinder 5 l. The fluid forced out of the rear end of the cylinder ii passes through the line H'i into the rear end of the cylinder l 32, forcing the piston l35 to the right to trip the reverse valve. As soon as the reverse alvev is'shifted, the pressure fluid will flow through the line ill, forcing the piston M forwardin the cylinder II and driving the,

fluid in the forward end of this cylinder through the line 5'55 into the rear end of the cylinder H. The fluid in the forward end of this cylinder is then forced through the line H5, the reverse and throttle valves into the line leading back to the The diamonds 25 and 25 move forward to- 'gether and rearwardly together when the units and the reverse valve are coupled as shown in Figure 3. The only change required to achieve this result is a change in the coupling of the connecting pipe lines.

'ZnjFigure 3, only one set of ball-check valves has been shown for the sake of clearness, but it will be understood that if it is desired to obtain a dwell of the trip-trimming tool 28' in engagement with the grinding wheel, then a second set of ball-check valves should be provided to operate in exactly the same manner as the second set used in the mechanism of Figure 2.

When two dresser units are coupled together as suggested inFigure 1, the relief valve 6! in the exhaust duct '55 of the valve-stem 35 is not required. The front ends of the two pistons M and l i are connected together and the difference in pressure on the front and rear faces of each piston is the same whether the piston be moving to the right or the left. Hence each diamond will V be moved at the same rate in one direction as in 'conditionwhich must be offset by the action of the relief. valve 6 I No particular mounting for the truing units and the reverse valve has been shown in any of the drawings, but it will be understood thatthey may be mounted in any suitable way and at any convenient location upon the grinding machine with which the truing units are to be used. It will be further understood that; while the diamonds 25 and 25', have been referred to as' side-trimming tools, one or other of them might, if desired, be used to dress the tip of a grinding wheel by a, reciprocating movement across the tip surface of the rotating wheel, in case it was not desired to use a tip-trimming tool similar to that shown at 28. It will be obvious, also, that instead of using two dressing'units, one of which carries both a side and a tip-trimming tool, that three dressing units mightbe coupled together, where it is desired to use a reciprocating trimming tool for the tip as well as the side surfaces of a wheel. The three units could be operated from one reverse and one throttle valve and might be identical in construction.

Certain features of the invention will have Wide applications and are not limited to use in dressing mechanisms. In general it may be said that the present application is intended to cover any adaptations, uses, orembodiments of the invention, following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and'as may be applied to the essential features hereinbefore set forth and as fall within the scope of the invention or the limits of the appended claims. a

. Having thus described our invention, what we claim is: V

1. In a dressing mechanism for a grinding wheel, a reciprocable member, a dressing 'tool meet with the wheel.

7 2. In a dressing mechanism for grinding wheels, a reciprocable member, a dressing tool mounted on said'memberfor dressing a side surface of the wheel, a dressing tool mounted on said member for dressing the tip surface of the wheel, said tip dresser being spaced from said side dresser far enough to allow the side dresser to complete its stroke before the tip dresser engages the wheel, means movable in opposite directions for moving the reciprocable member correspondingly in 0p-' posite directions, said last named means being.

manually operable in one direction to bring the two dressing tools successively into engagement with the grinding wheel, and means for automatically moving said means in the opposite direction after a dwell of the tip dressing tool in engagement with the wheel.

3. In combination, a support having a longitudinal bore formed eccentrically therein and having a longitudinal groove formed in its periphery at the point most remote from the center of said bore, a member shaped to fit said bore and reciprocable therein, a projecting member secured to said reciprocable member, and means carried by said projecting member adapted to engage in the groove of said support to guide said reciprocable member in its movements in the bore of said support.

4. In combination, a support of cylindrical shape having a cylindrical bore formed eccentrically therein and having a longitudinal groove formed in its periphery at the point most remote from the center of said bore, a cylindrical mem- P ber reciprocable in' said bore and having a sleeve secured thereto to surround said support, and a tongue carried by said sleeve adapted to engage in the peripheral groove of said support to guide said reciprocable member in' its movements.

5. In combination, a support having a cylinder formed therein and having a cylindrical guide projecting from one end of said'cylinder, said guide having a longitudinal cylindrical bore formed therein eccentrically of the periphery of said guide and having a longitudinal groove formed in its periphery at the point most remote from the center of said bore, a piston reciprocable in said cylinder, a piston-rod secured to said piston and. projecting from said cylinder through the bore of said guide, a sleeve secured to the outer end or said piston-rod to surround said guide, a tongue secured to the interior of said sleeve adapted to engage in a groove of said guide, a dressing tool secured to said piston-rod, and means for admitting fluid pressure alternately to opposite sides of said piston to reciprocate said dressing tool. a

6. In combination, a pair of cylinders and a piston reciprocable in each cylinder, a reverse valve controlling the direction of application of fluid pressure to said pistons, a duct connecting the reverse valve with one end of one cylinder, a duct connecting the other end of saidcylinder with one end of the other cylinder, means for moving the reverse valve manually in one direction, means for moving the reverse valve in the opposite direction, and a duct connecting the second end of the second cylinder with the last named means to apply fluid pressure to the last named means to operate the same on movement of the piston in one direction in the second cylinder.

'1. In combination, a support, a tubular memher having one end closed and adapted to slide telescopically on said support, a guard secured to said support and surrounding said tubular member, a valve carried by said support connecting with the outside air and adapted to be opened when the tubular member is moved outwardly on said support to admit air between the relatively telescoping members and adapted to be closed on reverse movement of said members, and means for reciprocating the tubular member on said support.

8. In combination, a cylinder and a piston reciprocable therein, a reverse valve having a longitudinal bore therein, supply and exhaust ducts leading to said valve, one of which connects with said bore, a throttle valve controlling the flow of fluid from said. here to the duct that connects therewith, a stop member limiting the opening of said throttle valve and having-a threaded connection with said reverse valve, means for holding the last named member against rotation, means connecting the reverse valve with opposite ends of said cylinder, said reverse valve being reciprocable to apply fluid pressure alternately to opposite ends of said piston, and said reverse valve being also rotatable to adjust said stop member.

9. In combination, a cylinder and a piston reciprocable therein, a reverse valve for controlling the direction of application of fiuid pressure to said piston, a second cylinder and a second piston reciprocable therein, means for moving the reverse valve in one direction, means operable by the second piston, after a predetermined movement in its cylinder, for moving the reverse valve in the opposite direction, and means whereby movement of the first piston in one direction in its cylinder operates to move the second piston in the last described direction in its cylinder.

10. In combination, a cylinder and a piston reciprocable therein, a reciprocable reverse valve for controlling the direction of application of fluid pressure to said piston, a second cylinder anda second piston reciprocabletherein, a plunger mounted in alignment with the second piston and spaced therefrom to be positively movable therebyafter a predetermined movement of the second piston in one direction, a duct connecting one end of the first piston to the reverse valve, a second duct connecting the other end of the first piston toone end of the second piston to move said second piston into engagement with the plunger on movement of the first piston in one direction in its cylinder, a duct connecting the opposite side of the second piston with the reverse valve, said reverse valve in its movement connecting the first and third ducts alternately with fluid pressure supply and exhaust, means operatively connecting the reverse valve andplunger to move one on movement of the other, means for resiliently holding the reverse valve at either limit of its movement, said last named means being disengageable in one direction on positive movement of the plunger and a coil spring interposed between the second piston and the plunger and adapted to be compressed on movement of the second piston into engagement withthe plunger and operable to shift the reverse valv'ethrough movement of said plunger after the resilient holding means has been disengaged.

11. In combination, a cylinder and a piston reciprocable therein, a reciprocable valve for controlling the direction of application of fluidpressure to said piston, a second cylinder and a second piston reciprocable therein, a plunger mounted in alignment with the second piston and spaced therefrom to be positively movable thereby after predetermined movement of the second piston in one direction, a duct connecting one end of the first piston to the reverse valve, a second duct connecting the other end of the first'piston to one end of the second piston to move the second piston into engagement with the plunger on movement of the first piston in-one direction in its cylinder, a duct connecting the opposite' side of the secondpiston with the reverse valve, auxiliaryducts connecting each of the first ducts with the first cylinder at points intermediate the length of said cylinder, a check valve cooperating with each of the auxiliary ductsto close the same against flow of fluid therethrough into said cylinder but permitting flowof fluid from said cylinder, a pivoted lever operatively connected at one end to the reverse Valve'and on'its opposite end to said plunger, said reverse valve in its movement connecting the first and thirdnamed ducts alternately with supplyand-exhaust lines, means'for resiliently holding the reverse valve at either limit of its movement, said means being disengageable in one direction on positive movement of the lever by engagement of said piston with said plunger, and a coiled spring interposed between the second piston and plunger and adapted to be compressed on movement of the second piston into engagement with the plunger to shift the reverse valve after the resilient holding means has been disengaged by movement of said lever.

12. In combination, a cylinder and a piston movable therein, a reverse valve controlling the movement of said piston, a second cylinder and a second piston movable therein, a single hydraulic connection from one end of one cylinder to one end of the other cylinder, hydraulic connections between said reverse valve and the other ends of the two cylinders, the operation of said valve causing supply and exhaust of the motive fluid alternately through the two last named hydraulic connections, means for moving said valve, in one direction, and means whereby when the second piston has moved a predetermineddistance in one direction in its cylinder, the reverse .valve is reversed.

13. In combination, a cylinder, a piston reciprocable therein and having a piston rod projecting' from one face thereof, a valve casing, a duct connecting the described face of piston with said casing, a second duct connecting the other face of the piston'with said casing at a point spaced from the point of connection of the first duct therewith, supply and exhaust lines connected to said casing, a reverse valve reciprocable in the casing to connect the supply and exhaust lines alternately with said two ducts, and a springclosed relief valve, and means whereby when the second, duct is connected to supply, said relief valve is interposed between the first duct and the exhaust line so that exhaust from the first duct is against the resistance of the spring operating said relief valve.

i l. In combination, a cylinder, a piston recip' rocable therein, a reciprocable valve for controlling the application of fluid-pressure alternately to opposite ends of the piston, manually operable means for moving the valve in one direction to admit the pressure fluid to one'end of the cylinder to move the piston in one direction, and means whereby the fluid flowing from the other end of said cylinder during said movement causes said valve to be reversed, after a predetermined dwell of the piston at the end of its movement in the first-mentioned direction, to reverse the movement of said piston.

15. In combination, a cylinder, apiston reciprocable therein, a reciprocable valve for controlling the application of fluid pressure alternately to opposite ends of the piston, a second cylinder, a piston reciprocable in said second cylinder, manually operable means for moving the valve in one direction, means connecting the second piston to said valve to move the valve in the reverse direction on movement of the second piston in one direction in its cylinder, and means connecting one end of the first piston with one end of the second piston to move the second piston in the described direction at the end of the movement of the first piston in its cylinder in the direction to which it is impelled on manual movement of the valve. 7 l

16. In combination, a cylinder, a piston reciprocable therein, a reciprocable valve for controlling the application of fluid pressure alternately to opposite ends of the piston, manually operable means for moving said valve in one dimotion to admit the pressure fluid to one end of said cylinder to move the piston in one direction, a second cylinder into which fluid flows from the opposite end of the first named cylinder as the piston moves therein in the described direction, a piston reciprocable in the second cylinder, and means operatively connecting the secondpiston to said valve to reverse said valve after a predetermined dwell of the first piston at the end of its movement in the described direction.

1'7. In combination, a cylinder, a piston reciprocable therein, a reciprocable valve for com trolling the application of fluid pressure alternately to opposite ends of the piston, manually operable means for moving the valve in one di-. rection to admit the pressure fluid to one end of said cylinder to move the piston in one direc-' tion, a second cylinder and a second piston reciprocable therein, means operatively connecting the second piston to said valve so that one moves the other, said last named means operating to move the second piston in one direction in the second cylinder on the above manual movement 7 of the valve, and means connecting the second cylinder with the end of the first cylinder which is on exhaust during movement of the first piston in the described direction, whereby to move the second piston in a direction to automatically reverse said valve.

18. In combination, a cylinder, a piston reciprocable therein, a reciprocable valve controlling the application of fluid pressure alternately to opposite ends of the piston, manually operable means for moving the valve in one direction to admit the pressure fluid to one end of said cylinder to move the piston in one direction, a second cylinder and a second piston reciprocable therein, means operatively connecting the second piston to said valve so that one moves the other, said last named means operating to move the second piston in one direction in its cylinder on the above described manual movement of the valve, the volumetric capacity of the second cylinder being greater than that of the first, means connecting the second cylinder with the end of the first cylinder which is on exhaust during movement of the first piston in the described direction, and means also connecting the pressure end of the first cylinder with the second cylinder after the first piston has bottomed in its cylinder on its first described movement, whereby to supply to the second cylinder the volume of the motive fluid required to automatically reverse said valve.

ROBERT S. CONDON. CLARENCE T. GALLOWAY. 

